This patent document relates to optical waveguides and devices based on optical waveguides.
Optical waveguides can be configured as either single-mode waveguides or multimode waveguides. A single-mode waveguide is structured to support and guide light in only one mode of propagation at a given optical frequency. In order to increase the data transmission capacity of such systems, multiplexing schemes are commonly used, such as Wavelength Division Multiplexing (WDM) where different signals are transmitted at different frequencies. When the optical power is below a certain power level, the waveguides and other structures are optically linear devices, the signals at different frequencies propagate independently with minimal cross talk.
Multi-mode waveguides support light in a given frequency in different optical modes of propagation. Different optical modes in such a multimode waveguide can have different optical properties. These modes are primarily defined at a given cross-section of the guiding structures and, as long as this cross-section is constant or changes slowly along the propagation direction, there is no conversion of light from one mode to another. In a simple straight multimode optical waveguide that supports two or more optical modes, two different optical modes usually exist independently and do not mix with each other. Bending of a multimode optical waveguide tends to cause mixing of different optical modes or inter-mode cross-talk.